Nowadays both the economic and environmental aspects guide the users of internal combustion engines to demand engines having as low specific fuel consumption as possible. Such a demand has led to the use of equipment increasing the charge of air in the engine cylinders compared to normally aspirated engines. A first piece of such equipment is generally called a supercharger whose main task is to increase the pressure or density of air, i.e. compress the air entering the engine cylinders. There are two main types of superchargers. A first one is a turbocharger, generally known as a turbo, which is a unit having, on the same shaft a turbine wheel and a compressor wheel such that the exhaust gases of the engine, by means of the turbine wheel, drive the compressor wheel, which compresses air into the cylinders. A second one is a mechanically driven supercharger, i.e. an air compressor, which is either directly or indirectly coupled to the engine crankshaft by means of a belt, a gear or a chain. A roots blower is a good example of mechanically driven superchargers. The superchargers are able to improve the specific fuel consumption of an internal combustion engine considerably, but a continuous strive to lower fuel consumption and lower emissions have led to the use of a second piece of equipment increasing the air charge. Such a piece of equipment is generally known as an intercooler, i.e. a device used for cooling the air compressed by a supercharger before the air enters the engine cylinders. In other words, a decrease in air intake temperature provides a denser intake charge to the engine and allows more air and fuel to be combusted per engine cycle, increasing the output of the engine.
There are two types of intercoolers, or Charge Air Coolers (or CAC) as the device is from now on called, used on supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through cooling. A first type is an air-to-air heat exchange device where the hot compressed air is cooled by means of outside ambient air. The use of ambient air results in a simple charge air cooler arrangement but has a few downsides. Firstly, the actual engine charge is directly proportional to the temperature of the ambient air, i.e. the higher is the outside temperature the smaller is the charge and vice versa. Secondly, the positioning of the engine, for instance in marine installations, requires considerable amount of ducting to lead the outside air to the charge air cooler. To avoid the above drawbacks, a second type of charge air cooler is an air-to-liquid heat exchange device where a specific cooling liquid circuit is arranged to be used in connection with the charge air cooler. The cooling liquid circuit includes means for keeping the temperature of the cooling liquid substantially constant irrespective of the ambient air temperature, whereby the air charge to the cylinders does not change as a function of the outside temperature. Thereby the engine's performance characteristics are the same irrespective of the geographical location of the engine. It is normal practice to use engine cooling liquid as the cooling liquid for the charge air, too. Thereby, the charge air cooling arrangement needs only one heat exchange device and some piping to operate properly, as the cooling liquid circuit for the engine coolant already comprises one or more heat exchange devices and thermostats.
However, it is quite clear that by using the engine cooling liquid the temperature of which is of the order of 90-100 degrees Celsius (° C.) the charge air temperature cannot be reduced but to a level of 100+° C. For example, if the charge air pressure is 4-4.5 bar, the temperature of the charge air after the compressor is some 170-190° C., whereby the temperature may be reduced by about 60-70° C. To be able to lower the charge air temperature further another cooling liquid circuit, so called low temperature (LT) cooling liquid circuit is often provided. In such a case the above discussed cooling liquid circuit utilizing hot engine cooling liquid is called a high temperature (HT) cooling liquid circuit. The low temperature cooling liquid circuit includes another air-to-liquid heat exchange device by means of which the temperature of the charge air may, preferably, be reduced to a value as low as possible, i.e. close to its dew point, which is, naturally, dependent on the humidity of the air. Heat exchange to such a low temperature requires the use of specific heat exchange arrangement in the low temperature cooling liquid circuit, where, for instance, outside air or water (from sea, lake or river) is used as the cooling medium.
It is well known in prior art to aim at keeping the temperature of the charge air as well as the heat exchange surfaces of the charge air cooler above the dew point of the charge air to prevent water from condensing on the heat exchange surfaces of the charge air cooler. If the charge air temperature is reduced below the dew point water condenses from the charge air. As an example of the generation of condensate on the heat exchange surfaces of the charge air cooler the following may be presented. At an ambient air temperature of 35° C. and a relative humidity of 80%, the content of water in the air is 0.029 kg water/1 kg dry air. If the air manifold pressure (charge air receiver pressure) under these conditions is 2.5 bar (=3.5 bar absolute), the dew point will be 55° C. If the air temperature in the air manifold is only 45° C., the air can only contain 0.018 kg water/1 kg dry air. The difference, 0.011 kg/kg (0.029−0.018) will appear as condensed water.
The condensed water is apt to cause both corrosion in the charge air system and inlet valves, and, at its worst, engine damage. The condensation of water may be fought by preventing the generation of the condensate, i.e. by following the pressure, humidity and temperature of the charge air and controlling the temperature and/or volume flow of the cooling liquid to such a level that the heat exchange surfaces of the charge air cooler stay at a temperature above the dew point and condensation does not occur. If, however, condensate is, for some reason, formed, additional problems related thereto may be avoided by providing the charge air cooler with means for draining the condensate out of the cooler.
For instance US-A1-2014290630 discusses methods and systems provided for draining condensate from a charge air cooler during a compressor bypass valve event. In one example, an engine controller may open a drain valve in the charge air cooler in response to potential compressor surge conditions. Opening the drain valve may be further based on an amount of condensate in the charge air cooler and a required decrease in pressure at an outlet of the compressor during the compressor bypass valve event.
A problem that requires periodical servicing of the charge air cooler is related to keeping the heat exchange surfaces of the charge air cooler clean such that the heat exchange capability of the heat exchange surfaces is not reduced. The intake air of an internal combustion engine contains always, in spite of the suction air filter upstream of the compressor, small particulates that tend to adhere gradually to all heat exchange surfaces they get into contact with. The small particulates may be fine sand, dust, exhaust gas particulates etc. that have passed the suction filter.
The prior art solution to the problem is either to clean the heat exchange surfaces manually, to use ultrasound or to arrange spray nozzles by means of which jets of cleaning fluid may be sprayed more or less automatically against the heat exchange surfaces. Such ways of cleaning have to be performed periodically, either in connection with ordinary servicing of the engine, or when the engine is running at low load.
The reduction in heat exchange capacity means, in practice, need for increased circulation of cooling liquid and somewhat more difficult control of the charge air temperature.